Be aware that if you are playing the game through Steam your save files are stored on the Steam cloud as well, so if you change your local copy manually it will create a conflict between the two versions and the game/Steam will ask you to resolve it.

Finally, I'll mention that starting from scratch is also possible by simply creating a new profile in-game. Simply click the sign that says "If this is not you, click here" on the top left of the game's menu as seen here: